In recent years, there has been a drive toward reducing the size of instrumentation used for analyzing and otherwise manipulating fluids (that is, liquid and gaseous materials). A reduced size offers several advantages, including the ability to analyze very small samples, increased analytical speed, the ability to use reduced amounts of reagents, and reduced overall cost.
Various articles or devices for microfluidic applications have been proposed. These devices typically include a glass or silicon substrate having a lithographically-patterned and etched surface that is provided with one or more structures to form a microfluid processing architecture. Polymeric or plastic substrates such as polyacrylates, polyesters, and polycarbonates have also been employed. In this case, the microfluid processing architecture is typically formed by microreplication of a structure on one surface of the plastic substrate.
For both the glass- and plastic-based devices, a structure forming the microfluid processing architecture is generally patterned onto a substantially planar surface of the substrate and must then be sealed with a cover plate, in order to complete the formation of the microfluid processing architecture and provide a device that typically has entrance and exit ports that provide fluid communication between the enclosed microfluidic architecture and the outside world. For glass or silicon substrates, the cover is typically made of glass and must be bonded to the lithographically-patterned surface at temperatures approaching 800° C. Often, the bonding is incomplete or the substrate cracks in the process. For plastic devices, the cover plate is typically another polymer film attached to the microreplicated surface of the device with adhesives or by solvent welding. Adhesives can introduce impurities and can affect the performance of the device, if they constitute one of the exposed surfaces of its enclosed microchannels. Solvent welding can introduce deformations in the microchannels of the fluid-handling architecture.
Thus, we recognize that there is a need for glass- and polymer-based microfluidic articles or devices that can be produced in such a way that the lamination of a cover plate can be avoided. We also recognize that there is a need for glass- and polymer-based microfluidic articles or devices having an increased density of microfluidic elements (for example, microchannels, mixing junctions, reaction microwells, separation channels, and detection zones) beyond what can be achieved with substantially planar microfluid processing architectures.